For the accommodations of freight and freight carrying aircraft, a lower deck and sometimes also an upper deck are fitted with a power driven system for loading freight supported on pallets into and out of the cargo areas. Typically, conveyor systems include a plurality of longitudinally extending roller trays rotatably supporting free roller conveyor wheels therein. At spaced intervals, power driven rollers are provided for engaging the roller surface of the pallet to move the pallet along the roller trays. These power driven rollers usually allow the roller to be raised and lowered relative to the lower surface of the pallet so that in the event of power failure, the power drive roller can be recessed to a retracted position and the freight moved along the roller trays.
Several systems have been utilized to control the power driven rollers. In a first system, a selector switch is provided and operatively connected to each of the power driven rollers. The selector switch is able to select a number of power driven rollers to be operated at a time. Available selection includes all power drive rollers on at one time, or all rollers on except for the last section. A second system operates all power driven rollers to be turned on and remain on until manually turned off. A third system powers all rollers. Upon latching of a pallet, the latch causes power to the roller to be discontinued. The power supply is routed through the latch and a switch therein, to motor. This will cause problems in recent developments wherein the latches are moveable within the freight carrier. This embodiment would require the wires to be moveable with the latches and avoid entanglement.
Another type of system is disclosed in U.S. Pat. No. 3,741,504, issued Jun. 26, 1973 in the name of Alberti et al. The patent discloses a cargo handling system utilizing free rollers and power drive wheels. The power driven wheels are activated all at one time and remain activated until manually disabled.
A problem with these prior art systems is that when rollers are activated under latched and stationary containers, wear occurs on the rollers located therebelow. Furthermore, power consumption of by all rollers operating at all times is undesirable.